The present invention relates to an ultrasonic proximity switch with an enabling output, which is connectable via a shared line to the enabling output of at least one additional ultrasonic proximity switch, and with an open-loop control block containing one input and one output.
When adjacent ultrasonic proximity switches operate, mutual interference can occur due to unfavorable reflections of the ultrasound in the surround field of the proximity switches. The echo-time measurement of an ultrasonic proximity switch is disturbed by the echo signal from a neighboring ultrasonic proximity switch when the ultrasonic proximity switches do not transmit synchronously. Therefore, correctly allocating the echo signals to those ultrasonic proximity switches which have output the corresponding initial pulses may not be possible. Since the switching output is set to be indefinite, echo-time evaluation errors occur.
Up until now, the known method for solving the above problem was to operate ultrasonic proximity switches serially, by cyclically connecting or disconnecting the voltage supplies to the ultrasonic proximity switches. The response time of the ultrasonic proximity switches is increased when this technique is used and is further delayed by internal reset times. Another wave mutual interference has been avoided up until now was to observe the standard mounting specifications, i.e., the specified minimum clearances for installing the ultrasonic proximity switches. However, the minimum clearances depend on the application desired. When avoiding mutual interference with a high degree of certainty is required, this method must be ruled out for many applications. Another solution for avoiding the mutual interferences consists in interconnecting the ultrasonic proximity switches by a shared line, so that a parallel synchronization takes place through this line. Another solution for avoiding mutual interference consists of interconnecting the adjacent operated proximity switches via their enabling output by a shared line so that a parallel synchronization takes place through this line. In this case, initial pulses are emitted at the same instant by all proximity switches, thereby mooting the problem of allocating the echo signals in a temporally correct manner to the respective ultrasonic proximity switches. Such a parallel synchronization is known, for example, from the company pamphlet (Honeywell MICRO SWITCH Units Information E 108/DB1067.2). However, with those proximity switches the echo-time evaluation of the unit does not contain any arranged evaluation algorithms and the unit is therefore fault-sensitive. Further, those proximity switches are not available as a standardized unit and do not permit serial synchronization.